Process for the production of a dna vaccine for cancer immunotherapy

ABSTRACT

The present invention relates to a method for producing a DNA vaccine for cancer immunotherapy comprising at least the steps of (a) transforming an attenuated strain of  Salmonella  with at least one DNA molecule comprising at least one expression cassette encoding at least one antigen or at least one fragment thereof; (b) characterizing at least one transformed cell clone obtained in step (a); and (c) selecting at least one of the transformed cell clone(s) characterized in step (b) and further characterizing said at least one selected transformed cell clone. The present invention further relates to a DNA vaccine obtainable by the method according to the present invention.

FIELD OF THE INVENTION

The present invention relates to a method for producing a DNA vaccine for cancer immunotherapy comprising at least the steps of (a) transforming an attenuated strain of Salmonella with at least one DNA molecule comprising at least one expression cassette encoding at least one antigen or at least one fragment thereof; (b) characterizing at least one transformed cell clone obtained in step (a); and (c) selecting at least one of the transformed cell clone(s) characterized in step (b) and further characterizing said at least one selected transformed cell clone. The present invention further relates to a DNA vaccine obtainable by the method according to the present invention.

BACKGROUND OF THE INVENTION

Attenuated derivatives of Salmonella enterica are attractive vehicles for the delivery of heterologous antigens to the mammalian immune system, since S. enterica strains can potentially be delivered via mucosal routes of immunization, i.e. orally or nasally, which offers advantages of simplicity and safety compared to parenteral administration. Furthermore, Salmonella strains elicit strong humoral and cellular immune responses at the level of both systemic and mucosal compartments. Batch preparation costs are relatively low and formulations of live bacterial vaccines are highly stable. Attenuation can be accomplished by deletion of various genes, including virulence, regulatory, and metabolic genes.

The attenuated Salmonella enterica serovar typhi Ty21a strain (short: S. typhi Ty21a), has been accepted for use in humans and is distributed under the trade name of Vivotif® (PaxVax Ltd, UK). This well-tolerated, live oral vaccine against typhoid fever was derived by chemical mutagenesis of the wild type virulent bacterial isolate S. typhi Ty2 and harbors a loss-of-function mutation in the galE gene, as well as other less defined mutations. It has been licensed as typhoid vaccine in many countries after it was shown to be efficacious and safe in field trials.

WO 2014/005683 discloses an attenuated strain of Salmonella comprising a recombinant DNA molecule encoding a VEGF receptor protein for use in cancer immunotherapy, particularly for use in the treatment of pancreatic cancer.

WO 2013/091898 discloses a method for growing attenuated mutant Salmonella typhi strains lacking galactose epimerase activity and harboring a recombinant DNA molecule.

Personalized oncology has the potential to revolutionize the way cancer patients will be treated in the future. The possibility to target patient specific tumor antigens and tumor stroma antigens is attracting increasing attention. A prerequisite for personalized cancer immunotherapy approaches are methods for the fast and cost-effective production of patient-specific cancer vaccines that meet the high medication safety standards.

Thus, there exists a great need for fast and robust manufacturing methods for cancer vaccines, in particular for patient specific cancer vaccines, which has not been met so far.

OBJECTS OF THE INVENTION

In view of the prior art, it is an object of the present invention to provide a novel method for the manufacture of a DNA vaccine for cancer immunotherapy, particularly for personalized cancer immunotherapy. Such a manufacturing method would offer major advantages for improving the treatment options for cancer patients.

SUMMARY OF THE INVENTION

In a first aspect, the present invention relates to a method for producing a DNA vaccine for cancer immunotherapy comprising at least the steps of (a) transforming an attenuated strain of Salmonella with at least one DNA molecule comprising at least one expression cassette encoding at least one antigen or at least one fragment thereof; (b) characterizing at least one transformed cell clone obtained in step (a); and (c) selecting at least one of the transformed cell clone(s) characterized in step (b) and further characterizing said at least one selected transformed cell clone.

In particular embodiments, the attenuated strain of Salmonella is of the species Salmonella enterica, more particularly of Salmonella typhi, most particularly of Salmonella typhi Ty21a.

In particular embodiments, the at least one expression cassette is a eukaryotic expression cassette.

In particular embodiments, said antigen is selected from the group consisting of a tumor antigen and a tumor stroma antigen, particularly selected from the group consisting of a human tumor antigen and a human tumor stroma antigen, more particularly selected from the group consisting of a human wild type tumor antigen, a protein that shares at least 80% sequence identity with a human wild type tumor antigen, a human wild type tumor stroma antigen and a protein that shares at least 80% sequence identity with a human wild type tumor stroma antigen. In a preferred embodiment, the antigen is a tumor antigen, more preferably a neoantigen.

In particular embodiments, said at least one DNA molecule comprises the kanamycin antibiotic resistance gene, the pMB1 ori, and a eukaryotic expression cassette encoding said antigen under the control of a CMV promoter, particularly wherein said DNA molecule is a DNA plasmid, more particularly wherein the DNA plasmid comprises the nucleic acid sequence as found in SEQ ID NO 1.

In particular embodiments, said attenuated strain of Salmonella is transformed by electroporation with said at least one DNA molecule comprising at least one expression cassette encoding at least one antigen or at least one fragment thereof in step (a).

In particular embodiments, step (b) comprises at least one of the following substeps (bi) through (biv): (bi) assessing the cell growth of at least one transformed cell clone obtained in step (a) over time; (bii) assessing the stability of the at least one DNA molecule comprising at least one expression cassette encoding at least one antigen or at least one fragment thereof in the at least one transformed cell clone obtained in step (a); (biii) isolating the at least one DNA molecule comprising at least one expression cassette encoding at least one antigen or at least one fragment thereof from at least one transformed cell clone obtained in step (a) and characterizing the at least one isolated DNA molecule by restriction analysis and/or sequencing; (biv) isolating the at least one DNA molecule comprising at least one expression cassette encoding at least one antigen or at least one fragment thereof from at least one transformed cell clone obtained in step (a), transfecting the at least one isolated DNA molecule into at least one eukaryotic cell and assessing the expression of the at least one antigen or the at least one fragment thereof in said at least one eukaryotic cell.

In particular embodiments, step (b) comprises one, two, three, or all four of said substeps (bi), (bii), (biii) and (biv).

In particular embodiments, step (c) comprises at least one of the following substeps (ci) through (cvi): (ci) assessing the number of viable cells per ml cell suspension of the at least one transformed cell clone selected in step (c); (cii) assessing the stability of the at least one DNA molecule comprising at least one expression cassette encoding at least one antigen or at least one fragment thereof in the at least one transformed cell clone selected in step (c); (ciii) isolating the at least one DNA molecule comprising at least one expression cassette encoding at least one antigen or at least one fragment thereof from the at least one transformed cell clone selected in step (c) and characterizing the at least one isolated DNA molecule by restriction analysis and/or sequencing; (civ) isolating the at least one DNA molecule comprising at least one expression cassette encoding at least one antigen or at least one fragment thereof from the at least one transformed cell clone selected in step (c), transfecting the at least one isolated DNA molecule into at least one eukaryotic cell and assessing the expression of the at least one antigen or the at least one fragment thereof in said at least one eukaryotic cell; (cv) testing for the presence of bacterial, fungal and/or viral contaminants in at the least one transformed cell clone selected in step (c); (cvi) verifying the bacterial strain identity of the at least one transformed cell clone selected in step (c).

In particular embodiments, step (c) comprises one, two, three, four, five, or all six of said substeps (ci), (cii), (ciii), (civ), (cv) and (cvi).

In particular embodiments, the presence of bacterial and/or fungal contaminants is tested in step (cv) by growing the at least one transformed cell clone selected in step (c) in or on at least one suitable selective medium.

In particular embodiments, the bacterial strain identity is verified in step (cvi) by growing the at least one transformed cell clone selected in step (c) on bromothymol blue galactose agar and/or on Kligler iron agar and/or by assessing the presence of Salmonella O5 and/or O9-surface antigen(s).

In a second aspect, the present invention relates to a DNA vaccine obtainable by the method according to the present invention.

In a third aspect, the present invention relates to the DNA vaccine according to the present invention for use in cancer immunotherapy.

DETAILED DESCRIPTION OF THE INVENTION

The present invention may be understood more readily by reference to the following detailed description of the invention and the examples included therein.

In a first aspect, the present invention relates to a method for producing a DNA vaccine for cancer immunotherapy comprising at least steps of (a) transforming an attenuated strain of Salmonella with at least one DNA molecule comprising at least one expression cassette encoding at least one antigen or at least one fragment thereof; (b) characterizing at least one transformed cell clone obtained in step (a); and (c) selecting at least one of the transformed cell clone(s) characterized in step (b) and further characterizing said at least one selected transformed cell clone.

The method according to the present invention allows for the rapid and cost-effective production of Salmonella-based DNA vaccines. The entire process including the generation of the antigen encoding DNA molecule, the transformation into the Salmonella recipient strain, the characterization of candidate clones and the selection and further characterization of the final DNA vaccine to be administered to the patient, takes less than four weeks, particularly less than three weeks, and typically as few as 16 days. Patient-specific DNA vaccines may conveniently be produced by small batch manufacture, which allows for the simultaneous generation, cultivation and characterization of several transformed Salmonella clones in parallel. Stepwise cell clone characterization maximizes product quality and minimizes process duration. The production process is highly robust and yields a safe and well-characterized DNA vaccine.

In the context of the present invention, the term “vaccine” refers to an agent which is able to induce an immune response in a subject upon administration. A vaccine can preferably prevent, ameliorate or treat a disease. A vaccine in accordance with the present invention comprises an attenuated strain of Salmonella, preferably S. typhi Ty21a. The vaccine in accordance with the present invention further comprises at least one copy of a DNA molecule comprising at least one expression cassette, preferably a eukaryotic expression cassette, encoding at least one antigen or at least one fragment thereof, preferably selected from a human tumor antigen, a fragment of a human tumor antigen, a human tumor stroma antigen, and a fragment of a human tumor stroma antigen.

According to the invention, the attenuated Salmonella strain functions as the bacterial carrier of the DNA molecule comprising an expression cassette encoding at least one antigen or at least one fragment thereof for the delivery of said DNA molecule into a target cell. Such a delivery vector comprising a DNA molecule encoding a heterologous antigen, such as a tumor antigen, a tumor stroma antigen or a fragment thereof, is termed DNA vaccine.

Genetic immunization might be advantageous over conventional vaccination. The target DNA can be detected for a considerable period of time thus acting as a depot of the antigen. Sequence motifs in some plasmids, like GpC islands, are immunostimulatory and can function as adjuvants furthered by the immunostimulation due to LPS and other bacterial components.

Live bacterial vectors produce their own immunomodulatory factors such as lipopolysaccharides (LPS) in situ which may constitute an advantage over other forms of administration such as microencapsulation. Moreover, the use of the natural route of entry proves to be of benefit since many bacteria, like Salmonella, egress from the gut lumen via the M cells of Peyer's patches and migrate eventually into the lymph nodes and spleen, thus allowing targeting of vaccines to inductive sites of the immune system. The vaccine strain of Salmonella typhi, Ty21a, has been demonstrated to-date to have an excellent safety profile. Upon exit from the gut lumen via the M cells, the bacteria are taken up by phagocytic cells, such as macrophages and dendritic cells. These cells are activated by the pathogen and start to differentiate, and probably migrate into the lymph nodes and spleen. Due to their attenuating mutations, bacteria of the S. typhi Ty21 strain are not able to persist in these phagocytic cells but die at this time point. The recombinant DNA molecules are released and subsequently transferred into the cytosol of the phagocytic immune cells, either via a specific transport system or by endosomal leakage. Finally, the recombinant DNA molecules enter the nucleus, where they are transcribed, leading to antigen expression in the cytosol of the phagocytic cells. Specific cytotoxic T cells against the encoded antigen are induced by the activated antigen presenting cells.

There is no data available to-date indicating that S. typhi Ty21a is able to enter the bloodstream systemically. The live attenuated Salmonella typhi Ty21a vaccine strain thus allows specific targeting of the immune system while exhibiting an excellent safety profile.

Attenuated derivatives of Salmonella enterica are attractive as vehicles for the delivery of heterologous antigens to the mammalian immune system because S. enterica strains can potentially be delivered via mucosal routes of immunization, i.e. orally or nasally, which offers advantages of simplicity and safety compared to parenteral administration. Furthermore, Salmonella strains elicit strong humoral and cellular immune responses at the level of both systemic and mucosal compartments.

In the context of the present invention, the term “attenuated” refers to a bacterial strain of reduced virulence compared to the parental bacterial strain, not harboring the attenuating mutation. Attenuated bacterial strains have preferably lost their virulence but retained their ability to induce protective immunity. Attenuation can be accomplished by deletion of various genes, including virulence, regulatory, and metabolic genes. Attenuated bacteria may be found naturally or they may be produced artificially in the laboratory, for example by adaptation to a new medium or cell culture or they may be produced by recombinant DNA technology. Administration of about 10¹¹ CFU of the attenuated strain of Salmonella according to the present invention preferably causes Salmonellosis in less than 5%, more preferably less than 1%, most preferably less than 1‰ of subjects.

In the context of the present invention, the term “comprises” or “comprising” means “including, but not limited to”. The term is intended to be open-ended, to specify the presence of any stated features, elements, integers, steps or components, but not to preclude the presence or addition of one or more other features, elements, integers, steps, components or groups thereof. The term “comprising” thus includes the more restrictive terms “consisting of” and “essentially consisting of”. In one embodiment the term “comprising” as used throughout the application and in particular within the claims may be replaced by the term “consisting of”.

The at least one DNA molecule comprising at least one expression cassette encoding at least one antigen or at least one fragment thereof is suitably a recombinant DNA molecule, i.e. an engineered DNA construct, preferably composed of DNA pieces of different origin. The DNA molecule can be a linear nucleic acid, or preferably, a circular DNA plasmid generated by introducing an open reading frame encoding at least one antigen or at least one fragment thereof into an expression vector plasmid.

In the context of the present invention, the term “expression cassette” refers to a nucleic acid unit comprising at least one antigen encoding gene or at least one fragment thereof under the control of regulatory sequences controlling its expression. The expression cassette comprised in the attenuated strain of Salmonella can preferably mediate transcription of the included open reading frame encoding at least one antigen or at least one fragment thereof in a target cell. Expression cassettes typically comprise a promoter, at least one open reading frame and a transcription termination signal.

In the context of the present invention, the term “transformed cell clone” refers to a cell population derived from a single cell colony obtained after Salmonella recipient strain transformation. Since the cells are derived from a single colony picked from a selection medium agar plate, it is assumed that all the cells derive from one single transformed Salmonella cell. However, the cell population derived from such a single colony obtained after transformation may comprise contaminants such as other bacteria, fungi or viruses.

In particular embodiments, the attenuated strain of Salmonella is of the species Salmonella enterica, more particularly of Salmonella typhi, most particularly of Salmonella typhi Ty21a.

In particular embodiments, the attenuated strain of Salmonella is of the species Salmonella enterica. In particular embodiments, the attenuated strain of Salmonella is Salmonella typhi Ty21a. The attenuated S. typhi Ty21a strain is the active component of Typhoral L®, also known as Vivotif® (manufactured by Berna Biotech Ltd., a Crucell Company, Switzerland). It is currently the only licensed live oral vaccine against typhoid fever. This vaccine has been extensively tested and has proved to be safe regarding patient toxicity as well as transmission to third parties (Wandan et al., J. Infectious Diseases 1982, 145:292-295). The vaccine is licensed in more than 40 countries. The Marketing Authorization number of Typhoral L® is PL 15747/0001 dated 16 Dec. 1996. One dose of vaccine contains at least 2×10⁹ viable S. typhi Ty21a colony forming units and at least 5×10⁹ non-viable S. typhi Ty21a cells.

One of the biochemical properties of the Salmonella typhi Ty21a bacterial strain is its inability to metabolize galactose. The attenuated bacterial strain is also not able to reduce sulfate to sulfide which differentiates it from the wild type Salmonella typhi Ty2 strain. With regard to its serological characteristics, the Salmonella typhi Ty21a strain contains the 09-antigen which is a polysaccharide of the outer membrane of the bacteria and lacks the 05-antigen which is in turn a characteristic component of Salmonella typhimurium. This serological characteristic supports the rationale for including the respective test in a panel of identity tests for batch release.

In particular embodiments, the S. typhi Ty21a recipient strain, i.e. the S. typhi Ty21a cells to be transformed with the at least one DNA molecule comprising at least one expression cassette encoding at least one antigen or at least one fragment thereof, can be generated based on commercially available Typhoral L® capsules without biochemical modification. After overnight culture on agar plates single colonies may be isolated and grown in 100 ml TSB culture medium overnight at 37° C. The cultures may then be formulated with 15% sterile glycerol, aliquoted (1 ml), labelled, frozen, and stored at −75° C.±5° C. as Master Cell Bank, pending use.

In particular embodiments, the bacterial strain identity of the thus obtained S. typhi Ty21a recipient strain may be verified by growing the strain on bromothymol blue galactose agar and/or on Kligler iron agar. The characteristics of S. typhi Ty21a colonies on such agar plates used as Master Cell Bank are described in Table 1.

In particular embodiments, the detection of bacteriophages may be performed by plating in soft-agar overlays containing an appropriate host and either the sample to be tested or a control suspension of phages. To improve the sensitivity of the assay a preceding enrichment step may be included. In this optional step the samples are incubated for 4 h with appropriate host cells. Subsequently, one sample of each of these enrichment cultures is plated.

TABLE 1 Characterization Testing of the Salmonella Typhi Ty 21a Isolates for Use as Master Cell Bank Test Parameter Test Method Ty21a colony characteristics Identity BTB-Gal Agar green to yellowish colonies without discoloration of the medium Kligler Iron Agar yellow coloration of the medium, no or only little gas formation Genome Identity - Corresponds to reference sequence Sequencing (Ty21a) Potency Growth Kinetics - pH in Corresponds to S. Typhi Ty21a Culture Medium Purity Bacteriophage Testing No phages detectable (SOP 97)

In particular embodiments, the viable cell number of the prepared recipient strain aliquots is from 10⁷ to 10¹¹, more particularly from 10⁸ to 10¹⁰, most particularly about 10⁹ CFU/ml.

In particular embodiments, the at least one expression cassette is a eukaryotic expression cassette. In the context of the present invention, the term “eukaryotic expression cassette” refers to an expression cassette which allows for expression of the open reading frame in a eukaryotic cell. It has been shown that the amount of heterologous antigen required to induce an adequate immune response may be toxic for the bacterium and result in cell death, over-attenuation or loss of expression of the heterologous antigen. Using a eukaryotic expression cassette that is not expressed in the bacterial vector but only in the target cell may overcome this toxicity problem and the protein expressed may exhibit a eukaryotic glycosylation pattern.

A eukaryotic expression cassette comprises regulatory sequences that are able to control the expression of an open reading frame in a eukaryotic cell, preferably a promoter and a polyadenylation signal. Promoters and polyadenylation signals included in the recombinant DNA molecules comprised by the attenuated strain of Salmonella of the present invention are preferably selected to be functional within the cells of the subject to be immunized. Examples of suitable promoters, especially for the production of a DNA vaccine for humans, include but are not limited to promoters from Cytomegalovirus (CMV), such as the strong CMV immediate early promoter, Simian Virus 40 (SV40), Mouse Mammary Tumor Virus (MMTV), Human Immunodeficiency Virus (HIV), such as the HIV Long Terminal Repeat (LTR) promoter, Moloney virus, Epstein Barr Virus (EBV), and from Rous Sarcoma Virus (RSV) as well as promoters from human genes such as human actin, human myosin, human hemoglobin, human muscle creatine, and human metallothionein. In a particular embodiment, the eukaryotic expression cassette contains the CMV promoter. In the context of the present invention, the term “CMV promoter” refers to the strong immediate-early cytomegalovirus promoter.

Examples of suitable polyadenylation signals, especially for the production of a DNA vaccine for humans, include but are not limited to the bovine growth hormone (BGH) polyadenylation site, SV40 polyadenylation signals and LTR polyadenylation signals. In a particular embodiment, the eukaryotic expression cassette included in the DNA molecule comprised by the attenuated strain of Salmonella of the present invention comprises the BGH polyadenylation site.

In addition to the regulatory elements required for expression of the heterologous antigen encoding gene, like a promoter and a polyadenylation signal, other elements can also be included in the recombinant DNA molecule. Such additional elements include enhancers. The enhancer can be, for example, the enhancer of human actin, human myosin, human hemoglobin, human muscle creatine and viral enhancers such as those from CMV, RSV and EBV.

Regulatory sequences and codons are generally species dependent, so in order to maximize protein production, the regulatory sequences and codons are preferably selected to be effective in the species to be immunized. The person skilled in the art can produce recombinant DNA molecules that are functional in a given subject species.

In particular embodiments, said antigen is selected from the group consisting of a tumor antigen and a tumor stroma antigen. Particularly, said antigen is selected from the group consisting of a human tumor antigen and a human tumor stroma antigen, more particularly from the group consisting of a human wild type tumor antigen, a protein that shares at least 80% sequence identity with a human wild type tumor antigen, a human wild type tumor stroma antigen and a protein that shares at least 80% sequence identity with a human wild type tumor stroma antigen. In particular embodiments, the at least one expression cassette encodes at least one fragment of at least one antigen, particularly at least one fragment of a tumor antigen and/or at least one fragment of a tumor stroma antigen, more particularly at least one fragment of at least one human tumor antigen and/or at least one human tumor stroma antigen, including fragments of proteins that share at least 80% sequence identity with a human wild type tumor antigen or a human wild type tumor stroma antigen. In particular embodiments, the at least one fragment of the at least one antigen comprises at least 5 consecutive amino acids of the reference antigen, more particularly at least 6, 7, 8, 9, 10, 15, 20, 25, amino acids of the reference antigen. In particular embodiments, the at least one antigen fragment comprises at least one epitope, more particularly at least 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 30, 40, 50, 60, 80 or 100 epitopes of the reference antigen. In particular embodiments, the at least one antigen fragment comprises from 1 to 100, or from 1 to 75, or from 1 to 50, or from 1 to 25 epitopes, in particular from 1 to 10 epitopes, more particularly from 1 to 5 epitopes. In the context of the present invention, the term “epitope” refers to a part of a given antigen that participates in the specific binding between the antigen and an antigen binding molecule such as an antibody. An epitope may be continuous, i.e. formed by adjacent structural elements present in the antigen, or discontinuous, i.e. formed by structural elements that are at different positions in the primary sequence of the antigen, such as in the amino acid sequence of the antigen protein, but in close proximity in the three-dimensional structure, which the antigen adopts, such as in the bodily fluid. According to the teaching of the present invention, the at least one fragment of the antigen may comprise any number of amino acids of the reference antigen, as long as the fragment of the antigen is immunogenic. Preferably, the immunogenicity of the at least one antigen fragment is reduced by less than 50%, less than 40%, less than 30%, less than 20%, less than 10%, less than 5% or less than 1% compared to the reference antigen, as measured by ELISA or as measured by ELISpot.

In the context of the present invention, the term “tumor antigen” refers to an antigen that is expressed in tumor cells. Typically, such tumor antigens are preferentially expressed by tumor cells, i.e. they are not or only weakly expressed by non-malignant cells or are only expressed in certain non-malignant tissues. In contrast, tumor stroma antigens are expressed by the tumor stroma, for instance by the tumor vasculature. One example of such a tumor stroma antigen is VEGFR-2, which is highly expressed by the tumor vasculature. In particular embodiments, the encoded VEGFR-2 antigen has the amino acid sequence as found in SEQ ID NO 2 or shares at least about 80% sequence identity therewith. Another example of a tumor stroma antigen is human fibroblast activation protein (FAP). The tumor antigens may be selected from known tumor antigens that are commonly expressed in a large proportion of cancers of a given type or of cancers in general. The term “tumor antigen” also comprises neoantigens, i.e. tumor-specific antigens that arise as a consequence of tumor-specific mutations. These neoantigens may either be patient specific or may occur in a number of cancer patients. In particular embodiments, the tumor antigen may be selected from the group consisting of human Wilms' Tumor Protein (WT1) having the amino acid sequence as found in SEQ ID NO 3 and a protein that shares at least about 80% sequence identity therewith, human Mesothelin (MSLN) having the amino acid sequence as found in SEQ ID NO 4 and a protein that shares at least about 80% sequence identity therewith, human CEA having the amino acid sequence as found in SEQ ID NO 5 and a protein that shares at least about 80% sequence identity therewith, CMV pp65 having the amino acid sequence as found in SEQ ID NO 6 and a protein that shares at least about 80% sequence identity therewith, CMV pp65 having the amino acid sequence as found in SEQ ID NO 7 and a protein that shares at least about 80% sequence identity therewith and CMV pp65 having the amino acid sequence as found in SEQ ID NO 8 and a protein that shares at least about 80% sequence identity therewith.

In particular embodiments, human VEGFR-2 has the amino acid sequence as found in SEQ ID NO 2, human Wilms' Tumor Protein (WT1) has the amino acid sequence as found in SEQ ID NO 3, human Mesothelin (MSLN) has the amino acid sequence as found in SEQ ID NO 4, human CEA has the amino acid sequence as found-in SEQ ID NO 5, and CMV pp65 has the amino acid sequence as found in SEQ ID NO 6, SEQ ID NO 7 or SEQ ID NO 8.

The tumor antigen and/or the tumor stroma antigen may also be a patient specific tumor antigen and/or tumor stroma antigen, i.e. an antigen that was shown to be expressed by tumor cells or the tumor stroma of one specific patient. Patient specific tumor antigens and/or tumor stroma antigens may be identified by assessing the expression profile of a patient's tumor and/or tumor stroma either on mRNA or on protein level. Alternatively, pre-existing T-cell immune responses to tumor antigens and/or tumor stroma antigens of a patient may be assessed. After having identified a patient specific tumor antigen and/or tumor stroma antigen, the method according to the present invention allows for the rapid manufacture of a safe, well characterized, patient-specific DNA vaccine suitable for cancer immunotherapy. Typically, the entire manufacturing process including the generation of the antigen encoding expression plasmid, the transformation into the Salmonella recipient strain, the characterization of candidate clones and the selection and further characterization of the final DNA vaccine to be administered to the patient, takes less than four weeks, particularly less than three weeks, and typically as few as 16 days.

In the context of the present invention, the term “protein that shares at least about 80% sequence identity with a tumor antigen or a tumor stroma antigen of a given sequence” refers to a protein that differs in the amino acid sequence and/or the nucleic acid sequence encoding the amino acid sequence of the given reference protein. The protein may be of natural origin, e.g. a homolog of the tumor antigen or the tumor stroma antigen, or an engineered protein. It is known that the usage of codons is different between species. Thus, when expressing a heterologous protein in a target cell, it may be necessary, or at least helpful, to adapt the nucleic acid sequence to the codon usage of the target cell. Methods for designing and constructing derivatives of a given protein are well known to anyone of ordinary skill in the art.

The protein that shares at least about 80% sequence identity with a tumor antigen or a tumor stroma antigen of a given amino acid sequence may contain one or more mutations comprising an addition, a deletion and/or a substitution of one or more amino acids, as compared to the given reference amino acid sequence. According to the teaching of the present invention, said deleted, added and/or substituted amino acids may be consecutive amino acids or may be interspersed over the length of the amino acid sequence of the protein that shares at least about 80% sequence identity a given tumor antigen or a tumor stroma antigen. According to the teaching of the present invention, any number of amino acids may be added, deleted, and/or substitutes, as long as the sequence identity with the reference tumor antigen or tumor stroma antigen is at least about 80% and the mutated tumor antigen or tumor stroma antigen protein is immunogenic. Preferably, the immunogenicity of the tumor antigen or the tumor stroma antigen that shares at least about 80% sequence identity with a reference tumor antigen or tumor stroma antigen of a given amino acid sequence is reduced by less than 50%, less than 40%, less than 30%, less than 20%, less than 10%, less than 5% or less than 1% compared to the reference tumor antigen or tumor stroma antigen of the given amino acid sequence, as measured by ELISA or as measured by ELISpot. Methods for designing and constructing protein homologues and for testing such homologues for their immunogenic potential are well known to anyone of ordinary skill in the art. In particular embodiments, the sequence identity with a given tumor antigen or tumor stroma antigen of a given amino acid sequence is at least about 80%, at least about 85%, at least about 90%, or most particularly at least about 95%. Methods and algorithms for determining sequence identity including the comparison of a parental protein and its derivative having deletions, additions and/or substitutions relative to a parental sequence, are well known to the practitioner of ordinary skill in the art. On the DNA level, the nucleic acid sequences encoding the protein that shares at least about 80% sequence identity with a tumor antigen or a tumor stroma antigen of a given amino acid sequence may differ to a larger extent due to the degeneracy of the genetic code.

In particular embodiments, said at least one DNA molecule comprises the kanamycin antibiotic resistance gene as a selection marker, the pMB1 ori, and a eukaryotic expression cassette encoding said antigen under the control of a CMV promoter, particularly wherein said DNA molecule is a DNA plasmid, more particularly wherein the DNA plasmid comprises the nucleic acid sequence as found in SEQ ID NO 1.

In particular embodiments, the DNA molecule is a recombinant DNA molecule derived from commercially available pVAX1™ expression plasmid (Invitrogen, San Diego, Calif.). pVAX1 is a plasmid vector for expression of proteins in eukaryotic cells which was specifically designed for use in the development of DNA vaccines by modifying the vector pcDNA3.1. Sequences not necessary for replication in bacteria or for expression of recombinant protein in mammalian cells were removed to limit DNA sequences with possible homology to the human genome and to minimize the possibility of chromosomal integration. Furthermore, the ampicillin resistance gene in pcDNA3.1 was replaced by the kanamycin resistance gene because aminoglycoside antibiotics are less likely to elicit allergic responses in humans.

The pVAX1™ vector contains the following elements: the human cytomegalovirus immediate-early (CMV) promoter for high-level expression in mammalian cells, the bovine growth hormone (BGH) polyadenylation signal for efficient transcription termination and polyadenylation of mRNA, and the kanamycin resistance gene as a selection marker.

In addition pVAX1™ contains a multiple cloning site for insertion of the gene of interest as well as a T7 promoter/priming site upstream and a BGH reverse priming site downstream of the multiple cloning site to allow sequencing and in vitro translation of the clones gene.

The commercially available pVAX1™ expression vector was further modified by replacing the high copy pUC origin of replication by the low copy pMB1 origin of replication of pBR322. The low copy modification was made in order to reduce the metabolic burden and to render the construct more stable. The generated expression vector backbone was designated pVAX10. Importantly, data obtained from transfection experiments using the 293T human cell line demonstrated that the kanamycin resistance gene encoded on pVAX10 is not translated in human cells. The expression system thus complies with regulatory requirements.

In particular embodiments, the at least one DNA molecule comprising at least one expression cassette encoding at least one antigen or at least one fragment thereof to be transformed into the attenuated Salmonella recipient strain is generated by cloning the at least one antigen cDNA or the at least one fragment thereof into the pVAX10 vector backbone. The vector backbone may be isolated from plasmid pVAX10.VR2-1, containing the cDNA for human VEFGR-2 cloned into the pVAX10 vector backbone. The VEGFR-2 cDNA can be excised from pVAX10.VR2-1 and the pVAX10 vector backbone may then be isolated by agarose gel electrophoresis.

In particular embodiments, synthesis of the cDNA insert is performed by double strand in vitro gene synthesis. The steps of the synthesis process are presented in FIG. 3.

In particular embodiments, said attenuated strain of Salmonella is transformed by electroporation with said at least one DNA molecule comprising at least one expression cassette encoding at least one antigen or at least one fragment thereof in step (a).

In particular embodiments, the S. typhi Ty21a strain Master Cell Bank (MCB) based on commercially available Typhoral L® capsules is used as starting strain for the preparation of the batch production clone. In order to obtain competent cells for electroporation the S. Typhi Ty21a MCB is resuspended in 500 ml of ice cold H₂O and centrifuged. After two further washes in ice cold water/10% glycerol the pellet is resuspended in 2 ml of 10% glycerol (animal free), aliquoted (50 μl) and frozen on dry ice. Competent cell batches are stored for maximum 4 weeks after at <−70° C. which a new competent cell batch is freshly produced. For transformation one aliquot of competent cells is thawed and electroporated in the presence of 3-5 μl of plasmid DNA encoding the desired antigen. Following a brief incubation period in 1 ml of LB (ACF) medium at 37° C., the cell suspension is streaked on LB (ACF) agar plates containing kanamycin (25 and 50 μg/mL). The plates are incubated at 37° C. overnight.

At least one single colony, typically from 1 to 10 colonies, particularly from 2 to 5 colonies are further tested to allow for the selection of at least one transformed cell clone for preparation of the batch production clone. Conveniently, three single colonies are used to inoculate 3 ml of LB medium (ACF soy peptone) containing kanamycin (50 μg/ml). Cultures are incubated at 37° C. overnight. Plasmid DNA is isolated and the selected clones are expanded in LB medium containing 50 μg/ml kanamycin. Cultures are mixed with 10% (v/v) glycerol, aliquoted (1 ml) and stored frozen at −70° C.

In particular embodiments, at least one of the following analytical parameters is evaluated in step (b) for selection of the batch production clone: growth kinetics over time upon culturing in selective medium determined by OD600, pH and CFU; plasmid stability after cryo-conservation (% PS); plasmid DNA extraction and confirmation of identity by plasmid restriction analysis; and determination of antigen expression efficacy after transient transfection of the plasmid DNA into an eukaryotic cell line. In particular embodiments, the batch production clone is then used to prepare drug substance (DS), which is then further characterized in step (c) to establish the final drug product (DP) to be administered to a patient.

Thus, in particular embodiments, step (b) comprises at least one of the following substeps (bi) through (biv): (bi) assessing the cell growth of at least one transformed cell clone obtained in step (a) over time; (bii) assessing the stability of the at least one DNA molecule comprising at least one expression cassette encoding at least one antigen or at least one fragment thereof in the at least one transformed cell clone obtained in step (a); (biii) isolating the at least one DNA molecule comprising at least one expression cassette encoding at least one antigen or at least one fragment thereof from at least one transformed cell clone obtained in step (a) and characterizing the at least one isolated DNA molecule by restriction analysis and/or sequencing; (biv) isolating the at least one DNA molecule comprising at least one expression cassette encoding at least one antigen or at least one fragment thereof from at least one transformed cell clone obtained in step (a), transfecting the at least one isolated DNA molecule into at least one eukaryotic cell and assessing the expression of the at least one antigen or the at least one fragment thereof in said at least one eukaryotic cell.

Particularly, step (bii) may be carried out after freezing and subsequent thawing of said at least one transformed cell clone.

Particularly, step (biv) may be carried out by transfecting HEK293T cells with plasmid DNA isolated from the single colonies obtained after Salmonella recipient strain transformation and performing Western blot analysis of the cell extracts using an appropriate antibody for the encoded antigen.

In particular embodiments, step (b) comprises one, two, three, or all four of said substeps (bi), (bii), (biii) and (biv).

In particular embodiments, step (b) comprises only substeps (bi), (bii) and (biii).

After consideration of the data obtained from growth characteristics, plasmid stability, plasmid identity and/or protein expression studies, at least one transformed cell clone is selected as the batch production clone. In particular embodiments, the batch production clone is then used to prepare the drug substance (DS), which is then further characterized in step (c) to establish the final drug product (DP) to be administered to a patient.

An outline of the manufacture of the Drug Product is depicted in FIGS. 1 and 2.

The manufacture of the Drug Substance (DS) may conveniently be carried out as described in the following: The DS is typically manufactured in compliance with GMP requirements. At least one batch production clone is transferred to three 50 ml flasks containing TSB medium plus 25 μg/ml kanamycin (Preculture 1). Colonies are grown to a maximum OD₆₀₀ of <1.0 for 9 h±1 h at 30° C. Agitation of each flask is set at 120 rpm. The flask with the highest OD value is selected for further cultivation. A volume of 50 ml of the Preculture 1 is transferred to a flask containing 1000 ml TSB medium plus 25 μg/ml kanamycin (main culture). After incubation at 30° C. for 9 h±1 h, with agitation set at 180 rpm, the bacteria are grown to a target OD₆₀₀ between 0.9 and 1.5. Once the fermentation is completed, glycerol is added to the culture to a final concentration of 15% (w/w). The suspension is mixed and then aliquoted (1 ml) into 2 ml cryovials. The vials are labelled and frozen immediately at −75° C.±5° C. for storage. It is to be understood that the described process workflow only describes one possible way to manufacture the Drug Substance. Of course, the process parameters, for example the culture volumes may be varied.

The Drug Substance is then further tested to dilute it to the final drug product concentration. Release specifications have been established for both, Drug Substance and Drug Product. At least one of the properties summarized in Table 2 and Table 3 are tested.

TABLE 2 Release Specifications for Drug Substance Test Test method Acceptance criterion Potency Viable Cell Count ≥10⁷ CFU/mL Plasmid Stability ≥66% Purity Microbial Impurity TAMC ≤10² CFU/mL EP 2.6.12/2.6.13 TYMC ≤20 CFU/mL (SOP M 073) Absence of the species in 1 mL: P. aeruginosa, S. aureus, E. coli, Clostridium sp. and other Salmonella Identity Bromothymol blue Colony growth in the presence of 1.25% galactose, galactose agar light blue transparent and/or green to yellowish colonies without colour change of the medium Kligler Iron-Agar Yellow coloring of the medium, no blackening, lack of H₂S formation Serological Test O9-positive O5-negative Plasmid Restriction analysis Determination of complete DNA-fragments after Identity restriction enzyme digestion with different DNA- nucleases corresponds to theoretical fragment lengths (±10%). DNA-Sequencing Corresponds to reference sequence (ATM-0274)

TABLE 3 Release Specifications for Drug Product Test Test method Acceptance criterion Potency Viable Cell Count ≥10⁷ CFU/mL Plasmid Stability ≥66% Identity Bromothymol blue Colony growth in the presence of 1.25% galactose agar galactose, light blue transparent and/or green to yellowish colonies without colour change of the medium Kligler Iron-Agar Yellow coloring of the medium, no blackening, lack of H₂S formation Serological Test O9-positive O5-negative

Thus, in particular embodiments, step (c) comprises at least one of the following substeps (ci) through (cvi): (ci) assessing the number of viable cells per ml cell suspension of the at least one transformed cell clone selected in step (c); (cii) assessing the stability of the at least one DNA molecule comprising at least one expression cassette encoding at least one antigen or at least one fragment thereof in the at least one transformed cell clone selected in step (c); (ciii) isolating the at least one DNA molecule comprising at least one expression cassette encoding at least one antigen or at least one fragment thereof from the at least one transformed cell clone selected in step (c) and characterizing the at least one isolated DNA molecule by restriction analysis and/or sequencing; (civ) isolating the at least one DNA molecule comprising at least one expression cassette encoding at least one antigen or at least one fragment thereof from the at least one transformed cell clone selected in step (c), transfecting the at least one isolated DNA molecule into at least one eukaryotic cell and assessing the expression of the at least one antigen or the at least one fragment thereof in said at least one eukaryotic cell; (cv) testing for the presence of bacterial, fungal and/or viral contaminants in at the least one transformed cell clone selected in step (c); (cvi) verifying the bacterial strain identity of the at least one transformed cell clone selected in step (c).

In particular embodiments, substep (cii) is carried out after freezing and subsequent thawing of said at least one transformed cell clone.

In particular embodiments, step (c) comprises one, two, three, four, five, or all six of said substeps (ci), (cii), (ciii), (civ), (cv) and (cvi).

In particular embodiments, step (c) comprises substeps (ci), (cii), (ciii), (cv) and (cvi).

Particularly, the number of viable cells may be determined by plating serial dilutions on agar plates. Conveniently, serial dilutions of the bacterial suspension down to a dilution factor of 10⁻⁸ are prepared and plated onto the agar plates. After appropriate incubation, colonies are counted. Counting should start, when colonies are clearly visible, but not too large.

Plasmid stability may be determined based on the kanamycin resistance of plasmid containing Salmonella bacteria. Growth of bacterial cells on TSB containing kanamycin indicates the presence of plasmids coding for the kanamycin resistance gene. Comparing the CFUs of the same sample plated on TSB plates with and without kanamycin allows the determination of the fraction of bacteria that carry the plasmid. Particularly, serial dilutions of the bacterial suspension are prepared and plated onto TSB plates optionally containing the antibiotic kanamycin. After appropriate incubation colonies are counted. Counting should start, when colonies are clearly visible, but not too large. The plasmid stability is calculated by comparing colony forming units on TSB with and without kanamycin as follows: PST=(CFU with kanamycin/CFU without kanamycin)×100.

Plasmid identity may be defined by the comparison of the size pattern of digested plasmid isolated from the vaccine strain with size markers. Particularly, the recombinant plasmid is isolated from the carrier and digested with at least one, typically at least two different digestion enzymes/combinations in separate reactions for an appropriate time. The reaction is stopped and analyzed on an agarose gel.

The identity of the genetic construct may further be determined through classical DNA sequencing of the plasmid. The sequence of the entire plasmid is determined by sequencing and is aligned to the original sequence of the plasmid. Particularly, the plasmid is prepared from Salmonella and quantified. It is then retransformed in E. coli, isolated, quantified and used for the sequencing reaction.

Expression of the at least one antigen or the at least one fragment thereof in eukaryotic cells may be verified by expression analysis after plasmid transfection into a eukaryotic cell line and Western blotting. Particularly, the recombinant construct is isolated from the carrier strain and used for transfection of a suitable eukaryotic permanent cell line. Due to the presence of a eukaryotic promoter, the encoding sequence is expressed. After suitable incubation, protein isolation and subsequent Western blotting, the presence of the recombinant protein is demonstrated and compared on a semi-quantitative basis with the reference material.

In particular embodiments, the presence of bacterial and/or fungal contaminants is tested in step (cv) by growing the at least one transformed cell clone selected in step (c) in or on at least one suitable selective medium. Particularly, in order to determine counts of total aerobic bacteria, molds and fungi and confirm the absence of the specific germs Escherichia coli, Salmonella sp., Pseudomonas aeruginosa, Staphylococcus aureus, and Clostridium sp. the sample may be tested in accordance with the monograph of the European Pharmacopoeia 04/2009:1055<Thyphoid Vaccine (Live, oral, strain Ty 21a)> using suitable selective media. Particularly, the test is conducted according to the European Pharmacopoeia Ph. Eur. monographs 2.6.12 and 2.16.13.

In particular embodiments, the bacterial strain identity is verified in step (cvi) by growing the at least one transformed cell clone selected in step (c) on bromothymol blue galactose (BTB-Gal) agar and/or on Kligler iron agar (KIA) and/or by assessing the presence of Salmonella 05 and/or 09-surface antigen(s).

The biochemical identity test relies on two selective media detecting biochemical properties (mainly galactose fermentation and sulfide production) of the microorganisms. In contrast to other Salmonella species, the attenuated vaccine strain Ty21a is not able to metabolize galactose. Growth on BTB-Gal-agar results in green to yellowish colonies without changing the colour of the medium. In contrast, cultivation of wild type Salmonella on BTB-Gal results in a strong yellow coloration of the media due to acid production during metabolization of galactose and subsequent colour change of the pH indicator (bromthymol blue). S. Typhi Ty21a can build morphological distinct sub-clones when growing on BTB-Gal. This additional type is characterized by decelerated growth of small, grey colonies upon and in-between the characteristic Salmonella colonies.

Kligler iron agar is used to differentiate members of the Enterobacteria. The features of this medium are based on the capability of the Enterobacteria to metabolize dextrose and lactose and to liberate sulphides. The Ty21a vaccine strain is able to metabolize dextrose indicated by a colour change of the pH indicator from red to yellow. However, strain S. Typhi Ty21a is not able to reduce sulfate to sulfide, while other Salmonellae blacken the colour of the media during hydrogen sulfide production and liberate gas which result in bubble formation within the agar. Growth of S. Typhi Ty21a can result in gas production, but is not typical for this strain. Organisms incapable of metabolizing either sugar like P. aeruginosa, do not alter the colour of the medium.

Particularly, bacterial strain identity may be biochemically verified as described in the following. A loop of the completely thawed suspension is transferred to the BTB-Gal-agar plates applying an appropriate streaking method to obtain single colonies. The inoculation of the control organism P. aeruginosa (ATCC 9027) and S. typhimurium (Moskau) is performed by transferring a bead of a Microbank® (storage system for microbial cultures) and subsequent streaking on the agar plate. For inoculation of KIA a loop (bead) of the same vial is first streaked onto the surface of the slant and then infeeded into the butt. The media are incubated for 48 h at 37° C.

The different serovars of the genus Salmonella can be differentiated using the appropriate polyclonal antisera or monoclonal antibodies. The attenuated recombinant S. Typhi Ty21a strain contains the 09-antigen which is a polysaccharide of the outer membrane. S. Typhi carries 09 but lacks 05 which is in turn characteristic of S. typhimurium. By combination of tests for the 05 and 09 antigens, the S. Typhi Ty21a strain can be well discriminated from other bacteria and particularly from wild type Salmonella species. Particularly, serotyping may be performed as described in the following. A drop of antiserum (05 or 09) is transferred to a chamber slide. A loop of colony containing material is taken from the lower (wet) side of the KIA and placed next to the antiserum. The solutions are mixed with the loop. The resulting suspension should be slightly turbid. The suspension is distributed by wiping of the chamber slides several times. The reactions are evaluated after 2 min against a black background.

In a second aspect, the present invention relates to a DNA vaccine obtainable by the method according to the present invention.

In a third aspect, the present invention relates to the DNA vaccine according to the present invention for use in cancer immunotherapy.

In particular embodiments, cancer immunotherapy comprises personalized cancer immunotherapy.

In particular embodiments, cancer immunotherapy further comprises administration of one or more further attenuated strain(s) of Salmonella comprising at least one copy of a DNA molecule comprising an expression cassette encoding a tumor antigen and/or a tumor stroma antigen, particularly wherein said one or more further attenuated strain(s) of Salmonella is/are Salmonella typhi Ty21a comprising a eukaryotic expression cassette, more particularly wherein said one or more further attenuated strain(s) of Salmonella comprise(s) an attenuated strain of Salmonella encoding human VEGFR-2 and/or human Wilms' Tumor Protein (WT1) and/or human Mesothelin (MSLN) and/or human CEA and/or pp65 of human CMV.

Combining two different tumor antigen and/or tumor stroma antigen targeting DNA vaccines may have synergistic antitumor effects. In particular, simultaneous targeting of different tumor antigens/tumor stroma antigens may minimize the risk of tumor escape. Combining a tumor antigen targeting DNA vaccine with a tumor stroma antigen targeting DNA vaccine may prove especially effective, since tumor cells and the tumor stroma are attacked at the same time.

In particular embodiments, the attenuated strain of Salmonella is co-administered with said one or more further attenuated strain(s) of Salmonella.

In the context of the present invention, the term “co-administration” or “co-administer” means administration of two different attenuated strains of Salmonella within three consecutive days, more particularly within two consecutive days, more particularly on the same day, more particularly within 12 hours. Most particularly, in the context of the present invention, the term “co-administration” refers to simultaneous administration of two different attenuated strains of Salmonella.

In particular embodiments, a patient may first receive a Ty21a-based DNA vaccine targeting a tumor antigen or a tumor stroma antigen that is commonly overexpressed in the type of cancer the patient is suffering from. During this “first line” treatment, a patient-specific tumor antigen and/or tumor stroma antigen may be identified. For this purpose the patient's tumor and/or stromal antigen expression pattern and/or the patient's pre-existing T-cell immune responses against tumor and/or stromal antigens may be assessed in a first step for example by companion diagnostics targeting the patient's specific tumor and/or stromal antigen pattern. The method according to the present invention then allows for the rapid establishment of a safe and well characterized patient-specific (personalized) DNA vaccine, which may be used as “second line”, or main treatment, only weeks after the identification of a patient-specific tumor antigen and/or tumor stroma antigen.

In particular embodiments, cancer immunotherapy is accompanied by chemotherapy, radiotherapy or biological cancer therapy. For cure of cancer, complete eradication of cancer stem cells may be essential. For maximal efficacy, a combination of different therapy approaches may be beneficial.

In the context of the present invention, the term “biological cancer therapy” refers to cancer therapy involving the use of living organisms, substances derived from living organisms, or laboratory-produced versions of such substances. Some biological therapies for cancer aim at stimulating the body's immune system to act against cancer cells (so called biological cancer immunotherapy). Biological cancer therapy approaches include the delivery of tumor antigens, delivery of therapeutic antibodies as drugs, administration of immunostimulatory cytokines and administration of immune cells. Therapeutic antibodies include antibodies targeting tumor antigens or tumor stroma antigens as well as antibodies functioning as checkpoint inhibitors, such as, but not limited to anti-PD-1, anti-PD-L1 and anti-CTLA4.

Chemotherapeutic agents that may be used in combination with the attenuated strain of Salmonella of the present invention may be, for example: gemcitabine, amifostine (ethyol), cabazitaxel, cisplatin, dacarbazine (DTIC), dactinomycin, docetaxel, mechlorethamine, streptozocin, cyclophosphamide, carrnustine (BCNU), lomustine (CCNU), nimustine (ACNU), doxorubicin (adriamycin), doxorubicin lipo (doxil), folinic acid, gemcitabine (gemzar), daunorubicin, daunorubicin lipo (daunoxome), procarbazine, ketokonazole, mitomycin, cytarabine, etoposide, methotrexate, 5-fluorouracil (5-FU), vinblastine, vincristine, bleomycin, paclitaxel (taxol), docetaxel (taxotere), aldesleukin, asparaginase, busulfan, carboplatin, cladribine, camptothecin, CPT-11, 10-hydroxy-7-ethyl-camptothecin (SN38), dacarbazine, floxuridine, fludarabine, hydroxyurea, ifosfamide, idarubicin, mesna, interferon alpha, interferon beta, irinotecan, mitoxantrone, topotecan, leuprolide, megestrol, melphalan, mercaptopurine, oxaliplatin, plicamycin, mitotane, pegaspargase, pentostatin, pipobroman, plicamycin, streptozocin, tamoxifen, temozolomide, teniposide, testolactone, thioguanine, thiotepa, uracil mustard, vinorelbine, chlorambucil and combinations thereof.

It may be also favorable dependent on the occurrence of possible side effects, to include treatment with antibiotics or anti-inflammatory agents.

Should adverse events occur that resemble hypersensitivity reactions mediated by histamine, leukotrienes, or cytokines, treatment options for fever, anaphylaxis, blood pressure instability, bronchospasm, and dyspnoea are available. Treatment options in case of unwanted T-cell derived auto-aggression are derived from standard treatment schemes in acute and chronic graft vs. host disease applied after stem cell transplantation. Cyclosporin and glucocorticoids are proposed as treatment options.

In the unlikely case of systemic Salmonella typhi Ty21a type infection, appropriate antibiotic therapy is recommended, for example with fluoroquinolones including ciprofloxacin or ofloxacin. Bacterial infections of the gastrointestinal tract are to be treated with respective agents, such as rifaximin.

In particular embodiments, the attenuated strain of Salmonella is administered before or during the chemotherapy or the radiotherapy treatment cycle or before or during biological cancer therapy, or before and during the chemotherapy or the radiotherapy treatment cycle or the biological cancer therapy. This approach may have the advantage that chemotherapy or radiotherapy can be performed under conditions of enhanced cancer immunity.

In particular embodiments, the attenuated strain of Salmonella is administered after the chemotherapy or the radiotherapy treatment cycle or after biological cancer therapy.

In particular embodiments, the attenuated strain of Salmonella is administered orally. Oral administration is simpler, safer and more comfortable than parenteral administration. In contrast, intravenous administration of live bacterial vaccines initially causes a bacteremia associated with safety risks of the sepsis-type and thus calls for careful observation and monitoring of clinical symptoms such as cytokine release. Oral administration of the attenuated strain of the present invention may at least in part overcome the described risks. However, it has to be noted that the attenuated strain of Salmonella of the present invention may also be administered by any other suitable route. Preferably, a therapeutically effective dose is administered to the subject, and this dose depends on the particular application, the type of malignancy, the subject's weight, age, sex and state of health, the manner of administration and the formulation, etc. Administration may be single or multiple, as required.

The attenuated strain of Salmonella of the present invention may be provided in the form of a solution, a suspension, lyophilisate, or any other suitable form. It may be provided in combination with pharmaceutically acceptable carriers, diluents, and/or excipients. Agents for adjusting the pH value, buffers, agents for adjusting toxicity, and the like may also be included. In the context of the present invention, the term “pharmaceutically acceptable” refers to molecular entities and other ingredients of pharmaceutical compositions that are physiologically tolerable and do not typically produce untoward reactions when administered to a mammal (e.g., human). The term “pharmaceutically acceptable” may also mean approved by a regulatory agency of a Federal or a state government or listed in the U.S. Pharmacopeia or other generally recognized pharmacopeia for use in mammals, and, more particularly, in humans.

The vaccine of the present invention is surprisingly effective at relatively low doses. In particular embodiments, the single dose is from about 10⁵ to about 10¹¹, particularly from about 10⁶ to about 10¹⁰, more particularly from about 10⁶ to about 10⁹, more particularly from about 10⁶ to about 10⁸, most particularly from about 10⁶ to about 10⁷ colony forming units (CFU). Administration of low doses of this live bacterial vaccine minimizes the risk of excretion and thus of transmission to third parties.

In this context, the term “about” or “approximately” means within a factor of 3, alternatively within a factor of 2, including within a factor of 1.5 of a given value or range.

In particular embodiments, the attenuated strain of Salmonella is for use in individualized cancer immunotherapy comprising the step of measuring the expression of at least one tumor antigen and/or at least one tumor stroma antigen and/or the pre-immune response against at least one tumor antigen and/or at least one tumor stroma antigen of a patient, for example by companion diagnostics targeting the patient's specific tumor and/or stromal antigen pattern.

SHORT DESCRIPTION OF FIGURES

FIG. 1: Overview over Drug Product manufacture

FIG. 2: Flow chart of Drug Product manufacture

FIG. 3: Expression plasmid synthesis

FIG. 4: VXM04 Clones Growth Kinetics—OD₆₀₀

FIG. 5: VXM04 Clones Growth Kinetics—CFU/ml

FIG. 6: VXM04 Clones Growth Kinetics—pH in Culture Medium

FIG. 7: VXM08 Clones Growth Kinetics—OD₆₀₀

FIG. 8: VXM08 Clones Growth Kinetics—CFU/ml

FIG. 9: VXM08 Clones Growth Kinetics—pH in Culture Medium

FIG. 10: VXM01 Clones Growth Kinetics—OD₆₀₀

FIG. 11: VXM01 Clones Growth Kinetics—CFU/ml

FIG. 12: VXM01 Clones Growth Kinetics—pH in Culture Medium

EXAMPLES Example 1: Synthesis of Antigen I Antigen Fragment Encoding cDNA

Synthesis of the cDNA inserts was performed by double strand in vitro gene synthesis. cDNAs encoding five different tumor antigens and one tumor stroma antigen were synthesized. The synthesized cDNAs are listed in Table 4.

TABLE 4 Synthesized antigen cDNAs cDNA cDNA length Antigen type cDNA SEQ ID Human wild type 4071 bp Full length wild type SEQ ID NO 9 VEGFR-2 tumor stroma antigen Human wild type 1893 bp Full length wild type SEQ ID NO 11 MSLN tumor antigen Human wild type 2109 bp Full length wild type SEQ ID NO 12 CEA tumor antigen Wild type human 1683 bp Full length wild type SEQ ID NO 13 CMV pp65 tumor antigen K436N mutated 1683 bp Full length mutated SEQ ID NO 14 human CMV pp65 tumor antigen Truncated K436N 1608 bp Truncated mutated SEQ ID NO 15 mutated human tumor antigen CMV pp65

The sequences of the cDNAs to be synthesized were subdivided into individual oligonucleotides of 40-50 bases. The designed oligonucleotides overlap and correspond to both DNA strands. These oligonucleotides were prepared by chemical synthesis. The in vitro synthesized forward and reverse oligonucleotides were combined in Eppendorf tubes and 5′-phosphorylated by incubation with T4 polynucleotide kinase and ATP. The phosphorylated forward and reverse oligonucleotides were denatured at 95° C. Complementary oligonucleotides were annealed by progressive cooling (1°/min) of the mixture. After the annealing process the aligned oligonucleotides were ligated using thermostable Taq DNA ligase. The denaturing and annealing process was repeated several times in a thermocycler to resolve mismatched base pairs and achieve complete matching of the complementary strands over the full length of the fragments. To increase the yield of the ligated fragments, PCR was performed after completion of the ligation step using primers annealing at outward positions of the fragments. The PCR amplification products were isolated by preparative agarose gel electrophoresis.

Example 2: Cloning of Antigen cDNA into Expression Plasmid

The cDNAs synthesized in Example 1 were cloned into the plasmid pVAX10 via NheI/XhoI.

The thus generated recombinant plasmids were transformed into E. coli, isolated and sequenced. The complete sequences of the synthesized plasmids were determined and aligned to the corresponding reference sequences. The results of the sequence verification are summarized in Table 5.

TABLE 5 Sequence verification of recombinant plasmids Identified mutations vs. cDNA reference sequence Human wild type VEGFR-2 none Human wild type MSLN 1 silent mutation Human wild type CEA none Wild type human CMV pp65 none K436N mutated human CMV pp65 none Truncated K436N mutated human CMV pp65 none

One mismatch mutation was detected in the open reading frame for hMSLN at plasmid position 1392 (adenine instead of guanine) corresponding to position 657 in the cDNA. This mute mutation (wobble position) does not result in an altered consensus amino acid for MSLN. The mutated sequence was therefore accepted for transformation of S. typhi Ty21a and generation of the batch production clones. For all other plasmids the cloned sequences displayed 100% sequence identity to the reference sequences.

Example 3: Transformation of S. typhi Ty21a with Antigen Encoding Plasmids

Salmonella typhi Ty21a was transformed with the five recombinant plasmids obtained in Example 2. For that purpose, single S. typhi Ty21a colonies were picked from agar plates and grown in 100 mL TSB culture medium overnight at 37° C. The cultures were then formulated with 15% sterile glycerol, aliquoted (1 ml), labelled, frozen, and stored at −75° C.±5° C. as Master Cell Bank, pending use. Two of the isolates prepared, designated VAX.Ty21-1 and VAX.Ty21-2, were selected for further use.

The bacterial strain identity of the prepared isolates was verified by growing the isolates on bromothymol blue galactose agar and/or on Kligler iron agar. The characteristics of the obtained cell colonies used as Master Cell Bank is described in Table 6.

TABLE 6 Characterization Testing of the Salmonella Typhi Ty 21a Isolates for Use as Master Cell Bank Test Result Parameter Test Method VAX.Ty21-1 VAX.Ty21-2 Identity BTB-Gal Agar Conforms, green to Conforms, green to yellowish colonies yellowish colonies without without discoloration of the discoloration of the medium medium Kligler Iron Agar Conforms, yellow Conforms, yellow coloration of the coloration of the medium, only little medium, only little gas formation gas formation Content CFU 7.6 × 10⁸ CFU/mL 7.0 × 10⁸ CFU/mL determination

The isolate VAX.Ty21-1 was used as recipient strain for transformation with the recombinant plasmids generated in Example 2. The frozen glycerol stock of isolate VAX.Ty21-1 was streaked on LB agar plates (ACF soy peptone). One single colony was picked and cultivated in 3 ml of LB-medium (ACF soy peptone) overnight at 37° C. This culture was used to inoculate 2×300 ml LB-medium which was further incubated at 37° C. until the OD600 reached 0.5. In order to obtain competent cells for electroporation the culture was harvested by centrifugation at 4° C. The pellet was resuspended in 500 ml of ice cold H₂O and centrifuged again. After two further washes in ice cold water/10% glycerol the pellet was resuspended in 2 ml of 10% glycerol (animal free), aliquoted (50 μl) and frozen on dry ice.

For transformation one aliquot of competent cells per recombinant plasmid was thawed and electroporated with 3-5 μl of recombinant plasmid DNA each. Following a brief incubation period in 1 ml of LB (ACF) medium at 37° C., the cell suspensions were streaked on LB (ACF) agar plates containing kanamycin (25 and 50 μg/ml). The plates were incubated at 37° C. overnight.

Three single colonies per transformation reaction were then selected and used to inoculate 3 ml of LB medium (ACF soy peptone) containing kanamycin (50 μg/ml). Cultures were incubated at 37° C. overnight. Plasmid DNA was isolated and plasmid identity was confirmed by restriction analysis.

The selected clones were expanded in LB medium containing 50 μg/ml kanamycin. Cultures were mixed with 10% (v/v) glycerol, aliquoted (1 ml) and stored frozen at −70° C. The plasmids of the recombinant Ty21a clones were isolated and complete sequencing was performed. 100% sequence identity of the plasmids of each of the selected clones with the reference sequence was confirmed except for the hMSLN clone were one silent point mutation was identified (see Tab. 5).

The generated transformed clones are listed in Table 7.

TABLE 7 Transformed Clones cDNA Batch Production Clones Human wild type VEGFR-2 VXM01: VAX.11-01, VAX.11-02, VAX.21-01, VAX.21-02, VAX.21-03 Human wild type MSLN VXM04: VXM04_K06424, VXM04_K06425, VXM04_K06426 Human wild type CEA VXM08: VXM08h_K08.1.1, VXM08h_K08.2.2, VXM08h_K08.4.4 Wild type human CMV pp65 VXM65_1: h_VXM65_K_K65.3.3 K436N mutated human CMV VXM65_2: h_VXM65_N_K65.4.12 pp65 Truncated K436N mutated VXM65_3: h_VXM65_Nshort_K65.1.1 human CMV pp65

Example 4: Characterization of Transformed Cell Clones and Batch Production Clone Selection

The following analytical parameters were evaluated for selection of the VXM01, VXM04 and VXM08 Batch Production Clones to be used for the establishment of the respective Drug Substances.

-   -   Growth kinetics over time upon culturing in selective medium         determined by OD600, pH and CFU     -   Plasmid stability after cryo-conservation (% PS)     -   Plasmid DNA extraction and confirmation of identity by plasmid         restriction analysis     -   Determination of antigen expression efficacy after transient         transfection of plasmid DNA into a eukaryotic cell line

The growth characteristics of the VXM01, VXM04 and VXM08 transformed clones listed in Table 7 were determined. All six VXM01 clones tested for growth expansion (VAX.11-01, VAX.11-02, VAX.21-01, VAX.21-02, VAX.21-03) grew well, but only clone VAX.11-02 grew to the same level as the Ty21a isolate from which it was derived. The growth characteristics of VXM04 clones VXM04_K06424, VXM04_K06425 and VXM04_K06426 are presented in FIG. 4, FIG. 5 and FIG. 6. All three clones displayed comparable growth rates in the culture medium with a slight growth advantage for clone VXM04_K06426. Regarding the VXM08 candidates (VXM08h_K08.1.1, VXM08h_K08.2.2 and VXM08h_K08.4.4), all clones displayed comparable growth characteristics, however, clone VXM08h_K08.1.1 was superior to the other two clones.

Testing of the six VXM01 clones revealed that plasmid stability of VAX.11-02 was highest followed by VAX.11-03 and VAX.21-02. No significant difference was apparent between the three VXM04 clones with respect to plasmid stability before and after freezing. Testing of the three VXM08 clones revealed that plasmid stability of VXM08h_K08.4.4 was highest followed by VXM08h_K08.1.1 and VXM08h_K08.2.2.

Restriction analysis of plasmid DNA isolated from each of the six VXM01 clones revealed the expected pattern of restriction fragments. Comparable amounts of plasmid DNA could be isolated from the three clones.

Restriction analysis of plasmid DNA isolated from each of the three VXM04 clones revealed the expected pattern of restriction fragments. Comparable amounts of plasmid DNA could be isolated from the three clones.

Restriction analysis of plasmid DNA isolated from each of the three VXM08 clones revealed the expected pattern of restriction fragments. Comparable amounts of plasmid DNA could be isolated from the three clones.

After transfection of HEK293T cells with plasmid DNA isolated from the six VXM01 clones and Western blot analysis of cell extracts all six clones expressed the VEGFR-2 protein, with VAX.11-02, VAX.11-03 and VAX.21-02 showing the highest level, and with VAX.11-02 exhibiting a trend towards higher expression level according to visual inspection of the bands in the Western Blot gel.

After transfection of HEK293T cells with plasmid DNA isolated from the three VXM04 clones and Western blot analysis of cell extracts three bands with apparent molecular weights of approximately 65 kDa, 40 kDa and 28 kDa were identified in each of the extracts. Based on staining intensity expression was highest when plasmid DNA isolated from clone 6316 was transfected.

After transfection of HEK293T cells with plasmid DNA isolated from the three VXM08 clones and Western blot analysis of cell extracts all 3 clones expressed the glycosylated human CEACAM5 protein, with clone VXM08h_K08.1.2 showing the highest level, according to visual inspection of the bands in the Western Blot gel.

Based on the data obtained from growth characteristics, plasmid stability, and protein expression studies, VAX.11-02 was selected as VXM01 Batch Production Clone for the preparation of the Drug Substance.

After consideration of the data obtained from growth characteristics, plasmid stability, and protein expression studies, clone VXM04_K06426 was selected as VXM04 Batch Production Clone for the preparation of the Drug Substance.

Based on the data obtained from growth characteristics, plasmid stability studies, clone VXM08h_K08.4.4 was selected as VXM08 Batch Production Clone for the preparation of the Drug Substance.

Example 5: Preparation and Release Testing of Drug Substances

The VXM01, VXM04 and VXM08 Drug Substances were manufactured in compliance with GMP requirements starting with a single colony of the selected Batch Production Clone each. Several cell suspension dilutions per Batch Production Clone were plated on TSB agar plates containing 25 μg/ml kanamycin (Preculture 1). The plates were incubated at 37° C. for 20-30 h. Upon completion of the incubation time, three single colonies each were selected and transferred to three 50 ml flasks containing TSB medium plus 25 μg/ml kanamycin (Preculture 2). Colonies were grown to a maximum OD600 of <1.0 for 9 h t 1 h at 30° C. Agitation of each flask was set at 120 rpm. The flask with the highest OD value was selected for further cultivation. A volume of 50 ml of the Preculture 2 was transferred to a flask containing 1000 mL TSB medium plus 25 μg/mL kanamycin (main culture). After incubation at 30° C. for 9 h t 1 h, with agitation set at 180 rpm, the bacteria were grown to a target OD600 between 0.9 and 1.5. Once the fermentation was completed, glycerol was added to the culture to a final concentration of 15% (w/w). The suspension was mixed and then aliquoted (1 ml) into 2 ml cryovials. The vials were labelled and frozen immediately at −75° C.±5° C. for storage.

The thus prepared Drug Substances VXM01, VXM04 and VXM08 were then further tested to establish the respective final Drug Products (release specification). The release characterization of the Drug Substances was based on the acceptance criteria listed in Table 3.

5.1 Biochemical Profile

For direct plating of Ty21a and Drug Substances VXM01, VXM04 and VXM08 a loop of the completely thawed suspension was transferred to BTB-Gal-agar plates applying an appropriate streaking method to obtain single colonies. The inoculation of the control organism P. aeruginosa (ATCC 9027) and S. typhimurium (Moskau) was performed by transferring a bead of a Microbank® (storage system for microbial cultures) and subsequent streaking on the agar plate. For inoculation of KIA a loop (bead) of the same vial was first streaked onto the surface of the slant and then infeeded into the butt. The media were incubated for 48 h at 37° C.

The resulting colonies showed the expected colony morphology. All three drug substances VXM01, VXM04 and VXM08 showed colony growth in the presence of 1.25% galactose on bromothymol blue galactose agar. The colonies were light-blue transparent and/or green to yellowish and did not result in colour change of the medium.

5.2 Serotyping

A drop of antiserum (05 or 09) was transferred to a chamber slide. A loop of cell material of each Drug Substance to be tested was taken from the lower (wet) side of the KIA and placed next to the antiserum. The solutions were mixed with the loop. The resulting suspension was slightly turbid. The suspension was distributed by wiping of the chamber slides several times. The reactions were evaluated after 2 min against a black background.

All three drug substances VXM01, VXM04 and VXM08 complied with the expected 09-positive and 05-negative serotype.

5.3 Restriction Analysis

The recombinant plasmids were isolated from the Drug Substances VXM01, VXM04 and VXM08 and digested with two different digestion enzymes/combinations in separate reactions for an appropriate time. The reactions were stopped and analyzed on an agarose gel. The Endonucleases used for the restriction analysis are presented in Table 8.

TABLE 8 Set-Up for Restriction Analysis Drug Restriction Substance Endonuclease Expected Size of Fragments (base pairs) VXM01 StyI 2209, 1453, 1196, 1094, 846, 623 and 159 VXM01 BamHI 7580bp VXM01 BgtI 2555, 2209, 1498 and 1318 VXM04 NheI/XhoI 1899 and 3494 VXM04 NdeI 1160 and 4233 VXM08 SacI 4142, 933 and 534 VXM08 BamHI 5609 VXM08 NheI/XhoI 3494 and 2115

All three recombinant plasmids isolated from Drug Substances VXM01, VXM04 and WM08 showed the expected restriction pattern.

5.4 Sequence Analysis of the Plasmid

The recombinant plasmids isolated from Drug Substances VXM01, VXM04 and VXM08 were quantified. After retransformation in E. coli, the recombinant plasmids were again isolated, quantified and sequenced.

100% sequence identity of the three recombinant plasmids with their respective reference sequence was confirmed.

5.5 Expression Analysis

The recombinant plasmids were isolated from Drug Substances VXM01, VXM04 and VXM08 using a commercial DNA extraction and purification kit and the DNA content was determined. One day before transfection 7.5×10⁵ 293 T cells were plated per well in 6-well plates to give a 90-95% confluence at the time of the assay. For transfection, the transfection complex consisting of the isolated plasmid DNA and Lipofectamine 2000™ was added to the cells and incubated for approximately 24 hours. After the incubation the cells were resuspended, washed once with PBS and lysed. Cell debris was pelleted by centrifugation. The supernatant was collected and protein content was determined. The samples were stored at −70° C. until Western Blot analysis was, performed. The presence of the recombinant proteins was demonstrated and compared on a semi-quantitative basis with appropriate reference material.

The expression levels of antigens VEGFR-2, MSLN and CEA were comparable to the chosen reference substance.

5.6 Viable Cell Number Determination

Serial dilutions of bacterial suspensions of Drug Substances VXM01, VXM04 and VXM08 down to a dilution factor of 10⁻⁸ were prepared and plated onto agar plates. After appropriate incubation colonies were counted. Counting was started, when colonies were clearly visible, but not too large.

The viable cell numbers determined are listed in Table 9.

TABLE 9 Viable cell numbers Drug Substance Viable cell number VXM01   3 × 10⁸ CFU/ml VXM04 5.5 × 10⁹ CFU/ml VXM08 2.5 × 10⁹ CFU/ml

5.7 Plasmid Stability

Serial dilutions of bacterial suspensions of Drug Substances VXM01, VXM04 and VXM08 (the same vials used for viable cell count testing) were prepared and plated onto TSB plates containing the antibiotic kanamycin. After appropriate incubation colonies were counted. Counting started, when colonies were clearly visible, but not too large. Plasmid stability was calculated by comparing colony forming units on TSB with and without kanamycin as follows:

PST=(CFU with kanamycin/CFU without kanamycin)×100

All three Drug Substances VXM01, VXM04 and VXM08 complied with the pre-set plasmid stability acceptance criterion as specified in Table 3. The determined plasmid stability of all three recombinant plasmids was at least 75%.

5.8 Microbial Impurities

To determine counts of total aerobic bacteria, molds and fungi and confirm the absence of the specific germs Escherichia coli, Salmonella sp., Pseudomonas aeruginosa, Staphylococcus aureus, and Clostridium sp. the Drug Substances VXM01, VXM04 and VXM08 were tested according to the European Pharmacopoeia Ph. Eur. monographs 2.6.12 and 2.16.13.

All three Drug Substances VXM01, VXM04 and VXM08 complied with the pre-set microbial impurity acceptance criterion as specified in Table 3. In all three Drug Substances VXM01, VXM04 and VXM08 the total aerobic microbial count (TAMC) was not more than 10² CFU/ml, the total yeast and mold count (TYMC) was not more than 2 CFU/ml and P. aeruginosa, S. aureus, E. coli, Clostridium sp. and other Salmonella strains were not detectable in 1 ml cell suspension.

5.9 Bacteriophage Testing

The testing procedure for the detection of bacteriophages employed plating in soft-agar overlays containing an appropriate host and either the sample to be tested or a control suspension of phages. To improve the sensitivity of the assay a preceding enrichment step was included. In this step the samples were incubated for 4 h with appropriate host cells. Subsequently, one sample of each of these enrichment cultures was plated.

All three Drug Substances VXM01, VXM04 and VXM08 complied with the pre-set purity of phage acceptance criterion as specified in Table 3. No phages were detectable in 100 μl of cell suspension after the enrichment step.

SEQUENCE TABLE

SEQ ID NO 1: expression plasmid SEQ ID NO 2: amino acid sequence VEGFR-2 SEQ ID NO 3: amino acid sequence WT1 SEQ ID NO 4: amino acid sequence MSLN SEQ ID NO 5: amino acid sequence CEA SEQ ID NO 6: amino acid sequence CMV pp65 SEQ ID NO 7: amino acid sequence CMV pp65 SEQ ID NO 8: amino acid sequence CMV pp65 SEQ ID NO 9: cDNA VEGFR-2 SEQ ID NO 10: cDNA WT1 SEQ ID NO 11: cDNA MSLN SEQ ID NO 12: cDNA CEA SEQ ID NO 13: cDNA CMVpp65 SEQ ID NO 14: cDNA CMVpp65 SEQ ID NO 15: cDNA CMVpp65 

1. Method for producing a DNA vaccine for cancer immunotherapy comprising at least the following steps: a) transforming an attenuated strain of Salmonella with at least one DNA molecule comprising at least one expression cassette encoding at least one antigen or at least one fragment thereof; b) characterizing at least one transformed cell clone obtained in step (a); c) selecting at least one of the transformed cell clone(s) characterized in step (b) and further characterizing said at least one selected transformed cell clone.
 2. The method of claim 1, wherein the attenuated strain of Salmonella is of the species Salmonella enterica, particularly of Salmonella typhi, more particularly of Salmonella typhi Ty21a.
 3. The method of claim 1 or 2, wherein the at least one expression cassette is a eukaryotic expression cassette.
 4. The method of any one of claims 1 to 3, wherein said antigen is selected from the group consisting of a tumor antigen and a tumor stroma antigen, particularly selected from the group consisting of a human tumor antigen and a human tumor stroma antigen, more particularly selected from the group consisting of a human wild type tumor antigen, a protein that shares at least 80% sequence identity with a human wild type tumor antigen, a human wild type tumor stroma antigen and a protein that shares at least 80% sequence identity with a human wild type tumor stroma antigen.
 5. The method of any one of claims 1 to 4, wherein said at least one DNA molecule comprises the kanamycin antibiotic resistance gene, the pMB1 ori, and a eukaryotic expression cassette encoding said antigen under the control of a CMV promoter, particularly wherein said DNA molecule is a DNA plasmid, more particularly wherein the DNA plasmid comprises the nucleic acid sequence as found in SEQ ID NO
 1. 6. The method of any one of claims 1 to 5, wherein in step (a) said attenuated strain of Salmonella is transformed by electroporation with said at least one DNA molecule comprising at least one expression cassette encoding at least one antigen or at least one fragment thereof.
 7. The method of any one of claims 1 to 6, wherein step (b) comprises at least one of the following substeps: bi) assessing the cell growth of at least one transformed cell clone obtained in step (a) over time; bii) assessing the stability of the at least one DNA molecule comprising at least one expression cassette encoding at least one antigen or at least one fragment thereof in the at least one transformed cell clone obtained in step (a); biii) isolating the at least one DNA molecule comprising at least one expression cassette encoding at least one antigen or at least one fragment thereof from at least one transformed cell clone obtained in step (a) and characterizing the at least one isolated DNA molecule by restriction analysis and/or sequencing; biv) isolating the at least one DNA molecule comprising at least one expression cassette encoding at least one antigen or at least one fragment thereof from at least one transformed cell clone obtained in step (a), transfecting the at least one isolated DNA molecule into at least one eukaryotic cell and assessing the expression of the at least one antigen or the at least one fragment thereof in said at least one eukaryotic cell.
 8. The method of claim 7, wherein step (b) comprises one, two, three, or all four of said substeps (bi), (bii), (biii) and (biv).
 9. The method of any one of claims 1 to 8, wherein step (c) comprises at least one of the following substeps: ci) assessing the number of viable cells per ml cell suspension of the at least one transformed cell clone selected in step (c); cii) assessing the stability of the at least one DNA molecule comprising at least one expression cassette encoding at least one antigen or at least one fragment thereof in the at least one transformed cell clone selected in step (c); ciii) isolating the at least one DNA molecule comprising at least one expression cassette encoding at least one antigen or at least one fragment thereof from the at least one transformed cell clone selected in step (c) and characterizing the at least one isolated DNA molecule by restriction analysis and/or sequencing; civ) isolating the at least one DNA molecule comprising at least one expression cassette encoding at least one antigen or at least one fragment thereof from the at least one transformed cell clone selected in step (c), transfecting the at least one isolated DNA molecule into at least one eukaryotic cell and assessing the expression of the at least one antigen or the at least one fragment thereof in said at least one eukaryotic cell; cv) testing for the presence of bacterial, fungal and/or viral contaminants in at the least one transformed cell clone selected in step (c); cvi) verifying the bacterial strain identity of the at least one transformed cell clone selected in step (c).
 10. The method of claim 9, wherein step (c) comprises one, two, three, four, five, or all six of said substeps (ci), (cii), (ciii), (civ), (cv) and (cvi).
 11. The method of claim 9 or 10, wherein in step (cv) the presence of bacterial and/or fungal contaminants is tested by growing the at least one transformed cell clone selected in step (c) in or on at least one suitable selective medium.
 12. The method of any one of claims 9 to 11, wherein in step (cvi) the bacterial strain identity is verified by growing the at least one transformed cell clone selected in step (c) on bromothymol blue galactose agar and/or on Kligler iron agar and/or by assessing the presence of Salmonella O5 and/or O9-surface antigen(s).
 13. A DNA vaccine obtainable by the method of any one of claims 1 to
 12. 14. The DNA vaccine of claim 13 for use in cancer immunotherapy.
 15. The DNA vaccine for use of claim 13, wherein the cancer immunotherapy comprises personalized cancer immunotherapy. 